Method of obtaining a three-dimensional map representation and navigation system

ABSTRACT

In a method for obtaining a three-dimensional map representation for a navigation system from digital, two-dimensional road map data, the road map data for a field of view that is to be represented and has a predetermined visual range are curved in a radially symmetric fashion about a virtual viewpoint by means of a polynomial transformation. A navigation system suitable for generating such a map representation is distinguished by a conversion unit with the aid of which two-dimensional road map data can be transferred into a view curved in a radially symmetric fashion.

CLAIM FOR PRIORITY

This application claims priority to International Application No.PCT/DE00/01422, which was published in the German language on May 5,2000, and which claims the benefit of priority to German Application No.199 207 09.7, filed in the German language on May 5, 1999.

The invention relates to obtaining a three-dimensional representationfor a navigation system from two-dimensional road map data, and to anavigation system which generates a three-dimensional representation.

BACKGROUND OF THE INVENTION

Digital road maps for navigation systems comprise two-dimensionalnetworks of road segments. A three-dimensional map output is desirablefor the purpose of better orientation, particularly in the case of a maprepresentation on a large scale.

U.S. Pat. No. 5,757,290 discloses a navigation system which represents aroad map from a bird's-eye perspective. The three-dimensional effect issupported by the use of colored variations dependent on distance.

Patent application EP 0 660 290 A1 relates to a three-dimensionalrepresentation from a bird's-eye perspective, in which different scalesare used for a near zone and a far zone.

Patent application EP 0 752 687 A2 discloses a three-dimensional (3D)representation from a bird's-eye perspective for navigation systems, inthe case of which application the transformation of digital road mapdata into the bird's-eye perspective is optimized by means of conversiontables.

The representation of a road map in the bird's-eye perspective isperformed by a perspective projection which is performed from a virtual,elevated viewpoint. The result is to produce a pseudo-3D effect whichcauses the plane to run together into a vanishing point. Thus, no actual3D information is used, but the plane is still flat.

Laid Open patent application DE 198 35 874 A1 discloses a map displayapparatus which is intended to render possible on a large-area map adirection-independent feeling for distance in conjunction with dynamiccompression of the map edges. A lateral transformation in the plane isundertaken for this purpose. A transformation into the third dimensiondoes not take place.

In one embodiment of the invention, there is a method for obtaining athree-dimensional map representation for a navigation system fromtwo-dimensional road map data having a network of road segments. Themethod includes, for example, obtaining road map data for a field ofview that is to be represented and has a predetermined visual rangebeing curved into the third dimension in a radially symmetric fashionabout a virtual viewpoint by a polynomial transformation.

In another aspect of the invention, the virtual viewpoint is determinedcontinuously by the navigation system, and the field of view is movedsynchronously with the virtual viewpoint.

In another aspect of the invention, objects are placed in the field ofview as three-dimensional geometric bodies.

In yet another aspect of the invention, the objects are provided with atexture.

In another aspect of the invention, the vehicle is represented in thefield of view.

In another aspect of the invention, the field of view is illuminated asat least one of a function of the time of day and the curvature of therepresented sections.

In still another aspect of the invention, a meshed network is displayed.

In another aspect of the invention, route segments of the road map dataare provided with boundary lines, and the boundary lines are distortedinto a curved course in the region of juxtaposed road segments.

In another embodiment of the invention, there is a navigation system.The system includes, for example, a display device, aposition-determining unit, a storage medium on which two-dimensionalroad map data is stored with the aid of a network of road segments, anda conversion unit to convert two-dimensional road map data from a fieldof view and has a predetermined visual range into a view curved in theshape of a dish.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages, features and possibilities of application of theinvention emerge from the following description of exemplary embodimentsin conjunction with the drawings, in which:

FIG. 1 shows a navigation system.

FIG. 2 shows a virtual viewpoint, the starting point for obtaining athree-dimensional map representation.

FIG. 3 shows a field of view resulting for the viewpoint of FIG. 1.

FIG. 4 shows various three-dimensional objects which are intended to beincorporated into a three-dimensional map representation.

FIG. 5 shows linear road segments of a two-dimensional road mapdatabase.

FIG. 6 shows road segments and points of intersection between roadsegments after their conversion into roads with boundary lines andsmoothing of the road contours.

FIG. 7 shows the operation of smoothing the road contours.

FIG. 8 shows an object before being fitted with a texture.

FIG. 9 shows the object of FIG. 8, with texture.

FIG. 10 shows the object of FIG. 9 set in a road map.

FIG. 11 shows a flowchart for generating a 3D image output.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides a method for obtaining a three-dimensionalrepresentation for a navigation system, and a navigation system, whichpermit an improved three-dimensional map representation.

A three-dimensional map representation with a particular natural effectis generated by using a polynomial transformation to transfer a planedefined by two-dimensional road map data into the third dimension. Thetransformation is generated in a radially symmetric fashion above avirtual viewpoint. This produces a three-dimensional distortion of theroad map data originally presented in two dimensions.

The artificial curvature or distortion of the two-dimensional road mapdata and, in particular, of the road network is generated by a nonlineartransformation and a perspective representative from an arbitrary,virtual viewpoint, preferably an instantaneous vehicle position.

A visual range or a horizon can be limited by a circular line, forexample. As a result, substantially fewer road map data need beconverted into a three-dimensional picture than in the case of a pureperspective projection. The limited field of view results in a clearrepresentation and a pleasant, dynamic 3D impression.

In a particular preferred embodiment, use is made of NURBS (Non-UniformRational B-Spline) surfaces are used for graphic display. Thesesubsurfaces can be used for any shape, in particular for the deformedthree-dimensional plane including the polygons which represent the roadsand intersections in the map representation.

Three-dimensional objects such as vehicles, buildings or other objectsare advantageously incorporated into a map representation. These objectscan be external objects which are not stored in the same medium as thedigital, two-dimensional road map data. The digital road maps areusually only geo information system databases in which geocoordinates ofroad segments, bodies of water and the like are stored in twodimensions.

Such objects can be stored, for example, as three-dimensional geometricbodies or structures. These bodies can be provided with textures inorder to evoke a natural impression. Moreover, the objects can berotated, for example when an object is passed.

The field of view to be represented and the visual range areadvantageously moved synchronously with the virtual viewpoint.

Whereas to date triangles have regularly been used to describe surfacesin the map representation of navigation systems, it is preferable to useNURBS surfaces for the representation of three-dimensional surfaces. TheNURBS surfaces can be described with the aid of very few parameters.Instead of a three-dimensional surface with, for example, 500*500 pointsin the x-y and z-planes being specified by means of triangles, a fewparameters typically suffice. These describe in an interpolated fashionthe edge of the surfaces (Bezier curves) and the approximate curvatureof the original data. Thus, NURBS surfaces can be used for veryefficient processing of the generated three-dimensional road map data orroad map networks.

The road segments, which are regularly stored only as lines in thedigital road map data, are preferably provided with boundary lines. Aparticularly realistic road view results in this case when the boundarylines in the regions of juxtaposed road segments are distorted into acurved course. This avoids an unnatural, angular representation ofjuxtaposed roads. The road segments are preferably initially treated inthis way and only subsequently distorted into a three-dimensional viewby means of a polynomial transformation.

A suitable measure for smoothing corners on juxtaposed road segments isa nonlinear interpolation. It is preferred in this case that points ofintersection between road segments or nodes for those points of aboundary line which lie closer to the point of intersection of two roadsegments to be further distant from the position determined by thedigital road map data than are points lying further distant from thepoint of intersection. Known functions with the aid of which this can beestablished are, for example, Bézier curves and polynomialinterpolations.

It is possible for road segments which are intended to acquire a curvedcourse of the road by means of shape points, to be processed in acorresponding way. The road segments, or their boundary lines,juxtaposed at the shape points are distorted by a nonlinearinterpolation in the region around these shape points. By contrast withroad segments which are juxtaposed at nodes, the distorted boundarylines should substantially lie on the shape points. That is to say, theboundary lines are not distorted directly at the shape point. Thedistortion around the shape points is preferably performed with the aidof a spline interpolation.

FIG. 1 illustrates a navigation system 1 having a main memory 11 and aconversion unit 12 constructed as a microprocessor. A distance meter 13and a direction meter 14 serve for determining position via deadreckoning. Just like the distance meter 13, the direction meter 14 and adrive 16 for a memory medium 161, a GPS sensor (not illustrated) isconnected to the microprocessor via a system bus 15.

The memory medium 161 is a DVD (Digital Versatile Disk).

A display device 17 is controlled via an image control unit 18 foroutputting image information and, in particular, for representing roadmaps. The image control unit 18 is connected, in turn, to themicroprocessor via the system bus 15.

FIG. 2 illustrates a vehicle position or a viewpoint S₀ which is aninstantaneous vehicle position determined by the navigation system.Starting from the measured vehicle position, the user of the navigationsystem is offered a map representation up to an artificial horizon of aheight t, this being done from a virtual viewpoint S which is projectedwith a height h above the viewpoint S₀.

An angle of view or a field of view α opens up from the virtualviewpoint S and reaches up to the artificial horizon. The distance r₁ upto the horizon, that is to say the visual range, is determined by thecamber or curvature of the plane and the start of the camber r₀. Onlythose points from the plane are distorted which are at a distance r fromthe viewpoint S₀ which is situated between r₀ and r₁.

The height h of the viewpoint S and the inclination β of the field ofview α can be selected arbitrarily. γ denotes the direction of view inthe representation. This determines the alignment of the field of viewα.

The road map data required for the representation are severely limitedby the horizon and the appropriate maximum visual range r₁ associatedtherewith.

A plane with road segments whose midpoint is the viewpoint S₀ is bent ordistorted in a radially symmetric fashion about the viewpoint S₀. Anonlinear interpolation of the two-dimensional plane takes place in thethird dimension. A polynomial function serves for the transformation.

A z-coordinate is determined for an arbitrary point with the Cartesiancoordinates x, y in the plane, in which casez=Σ _(i) a i*r ^(i)r=[(x−x _(p))²+(y−y _(p))²]^(1/2),the Cartesian coordinates x_(p) and y_(p) reproducing the vehicleposition S₀ determined by the navigation system. a_(i) are suitablecoefficients with i ε [1 . . . n].

A suitable polynomial transformation defined in a piecewise fashion andof degree p=6 for achieving a three-dimensional representation isreproduced below:

r>r ₀ : f(r)=−a(r−r ₀)^(p) +c(r−r ₀)²,$a = \frac{{- 2}t}{( {r_{1} - r_{0}} )^{p}( {2 - p} )}$$c = \frac{- {pt}}{( {r_{1} - r_{0}} )^{2}( {2 - p} )}$

r≦r ₀ : f(r)=0

The color of a point transformed into the third dimension remainsunchanged, and the texture, that is to say the representation of theroads, is maintained.

The polynomial transformation causes a representation of the field ofview α which is cambered or bent like a dish and has a defined, settablevisual range r₁. This visual range r corresponds to a horizon whichmoves synchronously with the change in the viewpoint S₀.

FIG. 3 illustrates a field of view α. Starting from the virtualviewpoint S, said field comprises only a subsection or sector of theroad map data which are situated around the virtual viewpoint S in acircle with the radius or the visual range r₁. The representation islimited to a field of view, situated in the driving direction, whichcorresponds to the natural way of viewing of a vehicle driver.

In order to make more accurate information on distances and scaleavailable to the viewer of the reproduced field of view α, the field ofview is provided with a mesh lattice, starting from the virtualviewpoint up to the visual range r₁ or the horizon.

The two-dimensionally represented road segments 2 and thethree-dimensional background can be represented in this case by NURBSsurfaces which are provided with textures.

In the left-hand part of the field of view α, the road map is reproducedin a distinctly brighter fashion, in order to reproduce the direction ofthe insolation as a function of the time of day. In addition, the regionof the strongest curvature is reproduced most brightly. A particularlyrealistic three-dimensional view is produced by this illumination as afunction of curvature.

FIG. 4 illustrates prominent objects 31 and a vehicle 33, which arestored separately from two-dimensional road map data of a geoinformation database. The objects 31 are intended for being incorporatedinto a map representation of the type described in FIG. 3.

A prominent object 31 is incorporated within the map representation withthe aid of the correct geo data. As the navigation system and thevehicle in which the navigation system is located approach, the objectis enlarged in accordance with the approach.

The objects which are recorded in a map representation are, for example,prominent buildings, towers, houses, bridges, columns, bends, castles,churches, museums, traffic lights, road signs or the like. The prominentobjects are stored in a main memory of the navigation system asthree-dimensional geometric figures in the form of vector graphics.

The objects are provided with a texture 32 in order to make them appearparticularly realistic. The texture is, for example, a scanned image ofthe relevant object. The texture 32 is laid over the associatedthree-dimensional object 31. Three-dimensional information of detailssuch as, for example, windows or balconies of a building, are alreadyincluded in the texture and so the three-dimensional geometric body needonly have the basic geometry or contours.

The objects 31 can be rotated, and so in the case of movement along theobject, the angle of view onto the object changes in a realistic way.

The vehicle 33 is projected into the field of view in the drivingdirection directly ahead of the virtual viewpoint. The type of vehicleillustrated and its texture 32 are freely selectable in the navigationsystem. Consequently, the vehicle 32 illustrated in the field of viewcan be of the same type as the real vehicle in which the navigationsystem is installed. In addition, the correct color of vehicle can beselected via the texture 32.

FIG. 5 illustrates a section of a digital road map which comprisestwo-dimensional road map data with a network of road segments 2. Aplurality of juxtaposed road segments have nodes or points ofintersection 23. Curves in the line of the road are fixed by shapepoints.

These two-dimensional road map data are stored on a commercial datamedium and constitute the basis for the three-dimensional maprepresentation.

FIG. 6 shows the same section of the digital road map after the roadsegments 2 have been provided by the conversion unit with boundary lines21. The boundary lines 21 are interpolated nonlinearly or distorted inthe region of juxtaposed road segments 2 or of points of intersection23. This distortion or bending of the line of the road can be produced,for example, by a Bézier curve or a polynomial interpolation.

The linear or stroke-shaped road segments 2, which are stored in thedigital road map, are reproduced as centerlines of the roadways.

By contrast with FIG. 5, at the points of intersection 23 and at shapepoints 22 the boundary lines no longer meet one another rectilinearly ata specific angle, but have bends or curves 24. The filled surfacesframed by roads are treated in the same way, with the result that theline of the road is smoothed and corners are rounded off.

FIG. 7 illustrates the smoothing of an angular road contour by means ofnonlinear interpolation with the aid of another section from the digitalroad map. The load segments 2 to be output have been provided again withboundary lines 21. Juxtaposed road segments 2 therefore acquire corneredcontours at the interfaces X between their boundary lines 21.

In order to avoid this, the boundary lines 21 are smoothed by means ofBézier curves in regions of juxtaposed road segments 2. Therepresentation of the Bézier curves is performed with the aid of the deCasteljau algorithm. The points b^(n)(t) of the Bézier curve are yieldedfrom:b _(i) ^(r)(t)=(1−t)b _(i) ^(r−1)(t)+tb _(i+1) ^(r−1)  (1),where {r=1, . . . , n; i=0, . . . , n−r} are given by the sequence ofpoints b_(i)(i=0, . . . ,n) as Bézier points of the Bézier polygon. Thepoints b_(i)(i=0, . . . ,n) are the control points which are prescribedby the geo coordinates of the road segments and define the course of theline, which is to be interpolated, of a boundary line at the interfacesX. A point on the Bézier curve corresponds to a parameter value t ε [0 .. . 1].

The points A1, A2, B1 and B2 represented are the control points b_(i)prescribed by the geo coordinates. More precisely, A1 and A2 are the endpoints of the Bézier curve represented. B1 and B2 are Bézierconstruction points. Furthermore, the prescribable parameters w1 and w2respectively signify distances for determining the positions of the endpoints A1 and A2, the starting point in each case being the appropriateinterface X.

FIG. 8 shows a three-dimensional geometrical object 31 which is achurch.

In FIG. 9, the three-dimensional object 31 is provided with a texture 32which had been obtained by scanning a photograph of this object. Thetexture contains detailed information on the object such as doors,windows, projections and the like. This detailed information isavailable in only two dimensions and is not transferred into athree-dimensional structure. Providing the three-dimensionally preparedobject 31 with the texture is enough to produce a convincingthree-dimensional effect.

FIG. 10 shows a section of a road map to be output after theincorporation of three-dimensional objects 31 and before thetransformation of the plane to be represented into a three-dimensionalview.

The objects 31 are already provided with the appropriate textures. Theroad segments 2 are fitted with boundary lines 21 and with smoothededges.

The sequence of the conversion of the initial data into a 3Drepresentation of a road map view is shown in FIG. 11.

The specified steps are executed for each representation of an imagesequence of a route calculated by the navigation system, in order togenerate a curved three-dimensional surface.

The first step is to generate the image background for a firstrepresentation.

Subsequently, the right-hand and the left-hand road boundary line(polygonal edge) are determined for all road segments to be illustratedusing the spline interpolation. The spline interpolation removes edgesin the line of the road.

Thereafter, the points of intersection (nodes) of the road segments arecalculated. The road boundary lines are distorted at the points ofintersection of the juxtaposed roads with the aid of Bézierinterpolation, in order to round off or smooth corners of juxtaposedroad segments.

Thereafter, the plane thus found, which consists of a multiplicity ofpolygonal surfaces which represent the image background and the roadsegments, is transferred into a three-dimensional representation. Asmall number of NURBS can be used as an alternative to the polygonalsurfaces. The three-dimensional coordinates of all the points of theboundary lines of the polygonal surfaces, or the NURBS are determined bythe deformation of the plane by means of polygonal transformation. Theresult obtained is output by means of perspective projection onto adisplay device.

1. A method for obtaining a three-dimensional map representation for anavigation system from two-dimensional road map data having a network ofroad segments, comprising: obtaining a field of view from thetwo-dimensional road map data, wherein the field of view is determinedby a plane in a form of a sector of a circle around a virtual viewpoint,and a radius of the circle corresponds to a predetermined visual range;and transforming the plane into a third dimension using a polynomialfunction such that the plane is concave in shape the polynomial functionbeingz=Σ _(i) a _(i) *r ^(i) ; r=[(x−x _(p))+(y−y _(p))²]^(1/2).
 2. Themethod as claimed in claim 1, wherein the virtual viewpoint isdetermined continuously by the navigation system, and the field of viewis moved synchronously with the virtual viewpoint.
 3. The method asclaimed in claim 1, wherein objects are placed in the field of view asthree-dimensional geometric bodies.
 4. The method as claimed in claim 3,wherein the objects are provided with a texture.
 5. The method asclaimed in claim 1, wherein the vehicle is represented in the field ofview.
 6. The method as claimed in claim 1, wherein the field of view isilluminated as at least one of a function of the time of day and thecurvature of the represented sections.
 7. The method as claimed in claim1, wherein a meshed network is displayed.
 8. The method as claimed inclaim 1, wherein route segments of the road map data are provided withboundary lines, and the boundary lines are distorted into a curvedcourse in the region of juxtaposed road segments.
 9. The method asclaimed in claim 1, wherein the filed of view is curved in the shape ofa dish.
 10. A navigation system, comprising: a display device; aposition-determining unit; a storage medium on which two-dimensionalroad map data is stored with the aid of a network of road segments; anda conversion unit to convert from the two-dimensional road map data afield of view, which is determined by a plane in a form of a sector of acircle around a virtual viewpoint, wherein a radius of the circlecorresponds to a predetermined visual range, into a three-dimensionalview by using a polynomial function such that the plane is concave inshape, the polynomial function beingz=Σ _(i) a _(i) *r ^(i) ; r=[(x−x _(p))+(y−y _(p))²]^(1/2).